This invention relates to an apparatus for measuring gobs of viscous liquid in free fall, and more particularly, to an apparatus using comparative and relative positioning measurements to determine if a gob is acceptable, while the gob falls from an orifice of a glass feeder.
In the manufacture of glass articles, molten glass is first supplied to a gob feeder. The feeder comprises a plunger which forces a molten stream of glass through an orifice. The gobs are separated at the orifice with shears prior to falling into the hopper of a glass forming machine. In order to control the manufacture of the glass articles, it is important to provide a means for measuring the weight and shape of the gobs of glass as they fall into the hopper, so as to determine if the gobs are acceptable.
One such method is described in U.S. Pat. No. 4,205,973. In this method the gobs fall through laser beams that activate perpendicularly arranged line cameras. These line cameras take successive scans of the gobs as the gobs fall through their field of view. The successive scans are combined to determine the outline of the falling gob. The system requires careful synchronization of the camera scanning speed with the motion of the gob to ensure that a complete scan is obtained for each passage. A slight variation in the speed of the gobs will cause an error in the measured size since the difference between scanning lines on the image, for a given scanning rate, depends on the velocity of the gob. In addition, variations in angular orientation also adversely affect the accuracy of measurements. Furthermore, a separate camera is required for each gob position.
There exists a need, therefore, in the gob measuring art for a gob measuring apparatus which captures the entire images of gobs during freefall and which is capable of measuring relative positioning with regard to other gobs and comparing the measured gob in terms of size and shape with other gobs and/or gob templates.